React Native for the little ones. Mobile Development Experience

Why do we need an application

• Flutter requires knowledge of Dart (an alternative to JavaScript). There was no time to study related technologies - I wanted to quickly “fly up” to test the hypothesis.
• Xamarin requires knowledge of C #. We have backend developers, but iOS and Android require different interfaces. Anyway, you have to duplicate the code and implementations.
• Native Script is designed to be bundled with Angular. Our project uses ReactJS and Redux, so no.
• React Native seemed cool, and they chose him. In addition, we just wanted to try it, despite the minuses and advantages of other solutions.

React native

• Cross-platform . We wanted to write the application initially under iOS, but the additional launch under Android is a huge plus.
• . , . React Native , 80% .
• . Telegram React Native 3000 . , , , .
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• You cannot add custom native modules.
• Expo is an abstraction layer over React Native. You cannot upgrade to a new version of the framework until Expo is updated.

In general, the choice is simple: we want to develop a prototype - we select Expo, we want an application with the prospect - React Native CLI.

We are writing an application

• Cross Platform : View, Text, Imageand others.
• Specific to each platform , for example, DatePickerIOSor DatePickerAndroid.

import React, {Component} from 'react';
import {Text, View, StyleSheet} from 'react-native';

export default class App extends Component {
    render() {
        return (
            <View style={styles.container}>
                <Image style={styles.image} source={require('./img/main.png')}/>
                <Text style={styles.welcome}>Hello, SEMrush!</Text>
            </View>
        );
    }
}

const styles = StyleSheet.create({
    container: {
        flex: 1,
        justifyContent: 'center',
        alignItems: 'center',
        backgroundColor: '#F5FCFF',
    },
    welcome: {
        fontSize: 20,
        textAlign: 'center',
        margin: 10,
    },
    image: {
        marginBottom: 20,
    },
});

Cross-platform

import {Platform, StyleSheet} from 'react-native';

const styles = StyleSheet.create({
    height: Platform.OS === 'ios' & 200 : 100,
});

import {Platform, StyleSheet} from 'react-native';

const styles = StyleSheet.create({
    container: {
        flex: 1,
        ...Platform.select({
            ios: {
                backgroundColor: 'red',
            },
            android: {
                backgroundColor: 'blue',
            },
        }),
    },
});

const Component = Platform.select({
    ios: () => require('ComponentIOS'),
    android: () => require('ComponentAndroid'),
})();

<Component />;

import {Platform} from 'react-native';

if (Platform.Version ===25) {
    console.log('Running on Nougat!');
}

import {Platform} from 'react-native';

const majorVersionIOS = parceInt(platform.Version, 10);
if (majorVersionIOS <= 9) {
    console.log('Work around a change in behavior');
}

Components

import React, { Component } from 'react';
import { Container, Header, Content, Button, Text } from 'native-base';
export default class ButtonThemeExample extends Component {
    render() {
        return (
            <Container>
                <Header />
                <Content>
                    <Button light><Text> Light </Text></Button>
                    <Button primary><Text> Primary </Text></Button>
                    <Button success><Text> Success </Text></Button>
                    <Button info><Text> Info </Text></Button>
                    <Button warning><Text> Warning </Text></Button>
                    <Button danger><Text> Danger </Text></Button>
                    <Button dark><Text> Dark </Text></Button>
                </Content>
            </Container>
        );
    }
}

Navigation

• react-navigation Facebook React Native.
• wix/react-native-navigation — Wix. , , -, — .
• react-router — react-router ReactJS . , .
• airbnb/native-navigation — - Airbnb. , .

• Flexible cross-platform solution.
• Native UI for each platform and native transitions between screens. We did not want to create an application that on Android looks like on iOS.
• It provides all the basic types of transitions: the lower tabs, swipe between screens, modal windows SwitchNavigator.

const HomeStack = createStackNavigator({
    Home: { screen: HomeScreen },
    Details: {screen: DetailsScreen },
});

const SettingsStack = createStackNavigator({
    Settings: { screen: SettingsScreen },
    Details: { screen: DetailsScreen },
});

const TabNavigator = createBottomTabNavigator({
    Home: { screen: HomeStack },
    Settings: { screen: SettingsStack },
});

export default createAppContainer(TabNavigator);

class HomeScreen extends React.Component {
    static navigationOptions = { title: 'Home' };

    render() {
        return (
            <View style={styles.container}>
                <Text>Home!</Text>
                <Button title="Go to Details" onPress={() => this.props.navigate('Details')}/>
            </View>
        );
    }
}

class SettingsScreen extends React.Component {
    static navigationOptions = { title: 'Settings' };

    render() {
        return (
            <View style={styles.container}>
                <Text>Settings!</Text>
                <Button title="Go to Details" onPress={() => this.props.navigate('Details')}/>
            </View>
        );
    }
}

class DetailsScreen extends React.Component {
    static navigationOptions = { title: 'Details' };

    render() {
        return (
            <View style={styles.container}>
                <Text>Details!</Text>
                <Button title="Go to Details" onPress={() => this.props.navigate('Details')}/>
            </View>
        );
    }
}

const Navigation = createAppContainer(TabNavigator);

//Render the app container component with the provider around it
export default class App extends React.Component {
    render() {
        return (
            <Provider store={store}>
                <Navigation />
            </Provider>
        );
    }
}

Need more components

Storage

Animations

export default class ProjectsScreen extends Component {

    state = {
        scrollY: new Animated.Value(
            Platform.OS === 'ios' ? -HEADER_MAX_HEIGHT : 0,
        ),
    };

    render() {
        const scrollY = Animated.add(
            this.state.scrollY,
            Platform.OS === 'ios' & HEADER_MAX_HEIGHT : 0,
        );
        const headerTranslate = scrollY.interpolate({
            inputRange: [0, HEADER_SCROLL_DISTANCE],
            outputRange: [0, -HEADER_SCROLL_DISTANCE],
            extrapolate: 'clamp',
        });

        return (
            <View>
                <Animated.View style={{ translform: [{ translatY: headerTranslate }] }}>
                    <SearchBar/>
                </Animated.View>
                <Animated.ScrollView
                    onScroll={Animated.event(
                        [{ nativeEvent: { contentOffset: { y: this.state.scrollY } } }],
                        { useNativeDriver: true },
                    )} contentInset={{
                        top: HEADER_MAX_HEIGHT,
                    }}
                    contentOffset={{
                        y: -HEADER_MAX_HEIGHT,
                    }}
                >
                    {this._renderScrollViewContent()}
                </Animated.ScrollView>
            </View>
        );
    }
}    

The problem of "flickering" of the screen at first start

Loss of connection

• Subscribe to events and, when changing the Internet connection, display messages to the user;
• check the quality of the connection;
• Check the type of connection (LTE, WiFi, 3G) for complex applications;
• Use a request to check your internet connection.

Application debugging

Connecting native modules

Result

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